Designing A Brick Arch
When constructing a brick arch, the first step
in the process is to draw the arch on paper.
The arch that was designed had an 8” rise which means that the diameter
was 16.” Another factor when designing
the arch and figuring out how the bricks needed to be cut was the fact that the
length of the bricks had to be 6” in order to fit the intended design.
Construction started by drawing the arch at a
1:1 scale. A bow compass was used to
draw the inside of the arch by pointing in the compass at the midpoint of the
16” line and extending it 8” out. Once
the inside dimension was drawn, the compass was extended an additional 6” to
provide the outer dimension of the bricks.
A compass then used to mark around the circumference of the arch to
determine how many bricks it would take to construct the desired arch. It was known the width of the bricks that
were used was 2 -5/8” and the joints were going to be 3/8.” In order to determine how many bricks were required,
a joint was drawn at the springing point of the left side arch, and a compass
set a 3” was pointed in on the top line of the joint and struck the next point
on the arch. This 3” setting accounted
for the thickness of the next brick and joint which was carried around the
outside line of the arch. When doing
this procedure, always strike the mark for the next brick and measure back for
the joint.
After passing the compass around the outside of
the arch, it was determined that 17 bricks were required to complete the
arch. The next step was to align a straightedge
that touched the midpoint of the arch line and the point on the outside of the
arch that indicated where a brick was to be placed and a line drawn from the
exterior to interior of the arch. This
produced the pie –shaped brick that need to be cut while keeping the joints
parallel to bricks.
Once the arch was drawn to full scale and deemed
to be functional, a template of the bricks was made out of card and provided
the angles for the brick cuts. The card
was placed over the arch and the process of using the compass and straightedge
was repeated to produce an accurate template.
Essentially, the drawing of the arch was repeated just enough to create
one full brick. A utility knife and
straightedge were then used to cut the card on a cutting mat.
Arch
Form
 |
| Side View of Form |
The arch form was created by drawing an
arch on ¾” plywood that was ½” shorter in diameter than the original. The
½” provided room for the arch to drop once the form was removed and accounted
for the thickness of the lath strips that enclosed the form. Two
identical arches, which provided the sides of the form, were drawn onto the
wood and cut with a jigsaw. A belt sander was used to smooth the cuts and
bring them down to the exact measurement line. The next step was building
the internal support blocks that would be used to fasten the form
together. The total with of the form needed to be around 5” in order to
match the thickness of a stone arch that would be flanking the brick arch once
constructed. Measurements were taken and found that the in order to match
the 5” stone arch, the internal supports needed to be about 3 -1/2” while
accounting for the 1 -1/2” total thickness of the plywood sides. A
centerline was then drawn on to divide the arch that was penciled on the
plywood. It was determined that 3 internal supports need to be placed
along the bottom of the interior of the form and 3 need to be placed around the
top of arch. In order to ensure equal placement, a 45⁰ triangle used
to divide the two sections to the left and right of the centerline. These lines were drawn and were aligned with
the center of each support block which provided uniform placement. Clamps were then used to fasten the blocks to
one side of the arch form. Screw holes
were counter sunk and the support blocks were attached the side. Once one side was attached to the internal
support, the other side was clamped on and screwed together to complete the
form. 3/16” thick lath that measured 5”
long were then cut to a width of 1 -1/2.”
These provided the outer covering of the arch and installed with
screws. The final step in the
construction of the form was to apply shellac.
This provided aesthetically pleasing finish while sealing wood from moisture
penetration.
 |
| Shellac Coating |
Designing a Jig
for Cutting Arch Bricks
 |
| Jig that Produces the Correct Cutting Angles |
The appearance of a brick arch relies
heavily on the cuts of the brick. While
arch can possible created without cutting the bricks, nothing compares to an
arch were each brick has been precisely cut.
Cutting begins by setting the angles that are dictated by the template
mentioned previously. A piece of plywood
was cut to match the dimensions of the cutting deck of the brick saw. The blade of the saw was run lightly over the
wood to establish the cutting width and placement of the blade. The dimensions of the brick were drawn on a
piece of card and the center line of the template was aligned with the center
line of brick. This produced the slices
that needed to be cut from each side of the brick. A second template was created with the slice
from one side of the brick removed. The
template was then aligned with the cut mark on the board and a piece of wood
was attached along the outer edge of the template to set the angle. A block of wood was attached at the back of
the cut line to provide a rest for the brick when being pushed through the
saw. This particular jig only provides
the angle for one cut of the brick, so the process was repeated to create a jig
that matched the other angle.
No comments:
Post a Comment